Inductance coil



Dec. 27, 1932. 8 L v 1,892,204

' INDUCTANCH COIL Filed Feb. 1, i930 E YZ INVENTOR CORNELIS 50L BY I g 7wzH L/ ATTORNEY Patented Dec. 27, 1932 I UNITED'STATES PATENT OFFICECORNELIS BOL, OF EINDHOVEN, NETHERLANDS, ASSIGNOR TO RADIO CORPORATIONOF AMERICA, A CORPORATION OF DELAWARE INDUCTANCE COIL Application filedFebruary 1,

The present invention relates to coils, and more particularly toimprovements in, or relating to, inductance coils for radio sets.

In constructing radio sets it is desirable that inductance coils beavailable, and that the external field of the coils be as feeble aspossible. Thus, a compact construction is assured For this purpose theso-called toroid coils are frequently used. These toroid coils have alimitation in that they'difi'er among themselves to a fairly markedextent as regards the value of-the. inductance, so that when mounting isnot possible to take the required number at will from among a greatnumber of coils, but a certain selection must be made, it beingnecessary to select sets of coils having matched values. This isespecially important if it is desired to operate a great number of tunedcircuits by means of one controlling device', as for example byarranging the rotors of a gang of condensers on a common shaft operatedby a single control. coils have the additional disadvantage of beingmechanically weak since the to mount these coils without a core, and byaccidental contacts, which obviously can never be avoided entirely, theinductance f ably of metal having a may become materially modified.

This invention provides a means for making the coils of the same type,so that all of them possess-the same inductance, and also retain it. Forthis purpose the coils are mounted in a screening case or shield,preferlow ohmic resistance, as for example, copper. Thus a coil isobtained which is mechanicallv protected, and the inductance of whichdoes not become modified byan accidental contact. is practicallyimpossible to make a great num; ber of coils having absolutely the sameinductance, the coil may be arranged in the screening case, in suchmanner that after the closing lid has been placed in position, the boxand lid have no longer between them interstices that give passage to afield, and the inductance can be varied from without the case.

This may, for example, be effected by mov- The proper position of the inwhich no undue couplings occur:

a number of equal coils in a set it Toroid practice is Since it i 1930,Serial No. 425,095, and in the Netherlands March 2, 1929.

ably arranging the coil itself, or an auxiliary osixed. adjustablemember may .be ascertained, for example, by inserting the coils of aseries, after they have been arranged in the screening case, one at atime into a permanent measuring installation, and varying the positionuntil the indicating instrument of the measuring installation takes theproper position. The adjusting members or the coil itself are then settightly in this position. Alternatively, the coil may be arranged in thecase at once so as to be stationary and the inductance may be varied bychanging the walls in form. Instead of an ordinary box an enclosureconsisting of two parts telescoping one within the other may serve asthe case.

The novel features which I believe to be characteristic of my inventionare set forth in particularity in the appended claims,.the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin connection with the drawing in which I have indicateddiagrammatically several organizations whereby my invention may becarried into effect.

The invention will be more clearly understood by reference to theaccompanying drawing in which an embodiment is illustrated.

In the said drawing,

Fig. 1 is a section of ascreening case with an elevation of the enclosedcoil,

Fig. 2 is a plan elevation view of the screening case, shown in Fig. 1with the strip 8 omitted,

Fig. 3 is a view similar to Fig. 1, but showing a modification,

Fig. 4 illustrates a view similar to Fig. 1, but showing a screeningcase having great resistance to deformation,

Fig. 5 shows a packing gland around the member, in the case. Once theproper tion is ascertalned, this posltion is.

terminal wire of the coil enclosed in the case,

ing case which may be of metal. The wall must be thick enough to preventany mechanical deformation. In addition, the case preferably should behermetically closed in order to ensure optimum screening. 2 designatesthe cylinder or core on which the coil is wound. The ends of the coilextend outwardly through tubes 4 and 5 secured to the case. 8 and 9designate metal strips which extend outwardly through slit-shapedapertures 6 and 7 respectively in the case 1. The case is entirelyclosed with the exception of the apertures 6 and 7 and the orifices ofthe tubes 4 and 5 so that the end walls have throughout a good metalliccontact with the cylindrical wall. lVhen the coil is disposed within thecase, as shown in Fig. 1, the coil is then connected to a measuringdevice and by means of the strips 8 and 9 the coil is shifted until theproper value of the inductance is attained. In this position the strips8 and 9 are soldered to the walls of the case so that the apertures 6and 7 are entirely closed.

If desired, one of the ends of the coil may be grounded to one of thestrips 8 or 9 or directly to the case itself and one of the tubes 4 or 5and the adjacent opening in the case may then be dispensed with.

To obtain more perfect screening the ends of the coil are led outthrough the tubes 4 and 5 but in some instances these tubes can bedispensed with.

The ends of the coil are preferably led out at points at which the fieldof the coil tends as little as possible to emerge, for example where thelines of force tend to pass parallel to the wall of the case as in theplanes of the coils as shown in Fig. 1.

Fig. 8 shows a different construction in which the coil is entirelymounted in a permanent and stationary manner in the case andthe'inductance is adjusted, by shifting by means of an adjusting screw10, a metal.

strip 12 secured to the lid or other part of the case.

In this case the coil is mounted on the case bottom by means of legs 13attached both to the core of the coil and to thecase.

Fig. 4 shows a screening case the end walls of which are spherical. Thishas the advantage that the mechanical resistance to change in form isgreater than in the case of flat end walls.

The screening case shown in Fig. 4 is entirely closed and only the endsof the coil are led out. The desired adjustment of the inductance isobtained by deformation. as for do not shift when the wall is example byforcing in one of the end walls, or otherwise changing its form. Thecore or other support of the coil is secured to one of the end walls bymeans of two straps 14. The straps are preferably secured at pointswhich changed in form to adjust the inductance. This may be assured bysoldering the straps to the end wall close to the border.

In this case the inductance may be adjusted in a very simple manner byplacing the case in a bench vise, connecting the coil in the stationarymeasuring device and adjusting the vise until the meter shows the propervalue of inductance. The measuring device may, for example, be anarrangement comprising a tuned circuit the inductance of which isconstituted wholly or partly by that of the coil to be measured. Thetuning is effected by varying the inductance. This method can be carriedout very rapidly and gives very reliable results. The arrangement shownin Fig. 4 has the advantage that, after ad ustment no soldering or othermanipulation of the coil is required. The end caps will hold theirdeformed shape when the pressure of the vise is removed.

Instead of convex the end walls may be concave in order to ensureresistance to change in form. The screening case may be such that one ofthe walls is little resilient and does not spring back after beingforced 1n.

convex end Walls consists in that the cases can be exhausted without anychange in form being produced varies.

In this case the apertures through which the ends of the coil are takenoutwards must be hermetically closed. This may be effected, for example,in the manner shown in Fig. 5. 1 is the wall of the screening case whichhas secured to it, for example by soldering. an inside cylindricalmember 18 and an outside sleeve 16. 15 designates a small sleeve or tubeof insulating material through which the wire 17 extends. The small cupformed by 16 is filled with some suitable cementing ma terial 19.

In order to ascertain whether the case is hermetically closed it mayhave mounted on it a conventional cylindrical valve member 20 adapted tobe joined to the elastic tube of an air pump.

The screening cases may be exhausted and then filled with dry air. Thusone can avoid water vapour which otherwise might be present within thecase and be precipitated on a decrease in temperature. In this case theshield or screen must likewise be hermetically closed.

If the case consists of two parts 21 and 22 telescoping one within theother, as shown in Fig. 6, provision should be made for the walls of theparts that slide one within the other overlapping each other in order toprevent the field of the coil from emerging. In this case the inductancemay be corrected by more or less slipping the parts one within theother.

An additional advantage of concave or as the barometric pressure As arule only such a thin layer of metal is required for the electricscreening that the mechanical protection would not be ensured thereby.In order to ensure the necessary mechanical strength the metal may bethicker than is required for the electric screening, but as analternative the case may consist of insulating material and internallycoated with metal. Alternatively, the case may be of metal such as ironand internally coated with a thin layer of very good conducting metal,for example silver.

The described method of mounting the coils has the great advantage thatcoils are obtained having practically equal inductance, occupying verylittle space and being adapted to be arranged in close proximity to eachother without there being any risk of undue magnetic or electrostaticcoupling.

In order to make the entire set as compactas possible the switches maybe mounted on the screening cases, which ensures the advantage of Veryshort connections. The connections to the condensers may likewise bevery short.

While I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications in the arrangements; aswell as in the apparatus employed, may be made without departing fromthe scope of my invention as set forth in the appended claims.

WVhat I claim is:

1. A method of producing a shielded inductance coil which consists.indisposing an inductance coil within a shielding container, adjusting thespatial relationship between the said container and said coil to adjustthe value of the coil inductance to adesired quantity, and evacuatingthe container.

2.. A method of producing a shielded inductance coil which consists indisposing an inductance coil within a metallic, shielding container,adjusting the spatial relationship between the walls of said containerand said coil to adjust the value of the coil inductance to a..-predetermined quantity, evacuating the container, and filling theinterior of the latter with dry air.

3. A method of producing a shielded inductance coil which consists indisposing an inductance coil within a shielding container, and bodilydisplacing the 'C0il relative to the container walls to adjust the valueof the coil inductance to a predetermined quantity.

4. A method of producing a shielded inductance coil which consists indisposing an induc ance coil within a shielding container, varying thespatial relationship between at least one of the walls and the coiltoadjust the value of the coil inductance to a predetermined quantity,and evacuating the container.

5. A method of producing a shielded inductance coil which consists indisposin an inductance coil within a metallic, shiel ing container,afiixing the coil to at least one of the walls of the container, varyingthe spatial relationship between at least one of the walls and the coilby deforming said wall to adjust the value of the coil inductance to apredetermined quantity, and exhausting the container.

6. A method of producing a shielded inductance coil which consists indisposing an inductance coil within a shielding conta ner provided withterminal outlets, extending the terminals of the coil through saidoutlets, and bodily moving the coil relative to all the walls of thecontainer to adjust the value of the coil inductance to a predetermineduantity.

7 In combination, a metallic, s ielding container provided with a pairof openings, an inductance coil disposed within the interior of thecontainer and having its terminals extending through the said openings,and means including a movable support for. the coil for displacing thecoil within the container to a desired position.

CORNELIS BOL.

